1. Field of the Invention
The invention pertains to television information transmission and reception and more particularly to the transmission and reception of high definition television information.
2. Description of the Prior Art
Conventional color television systems transmit picture information at a rate of 59.94 picture fields per second, two constituting a frame, each frame consisting of 525 horizontal scan lines. To reduce the transmission and reception bandwidths required to reproduce the transmitted picture, these horizontal scan lines are interlaced from field-to-field with a ratio of two-to-one, that is only every other scan line is transmitted in each field. Scan lines omitted in one field are transmitted in the next succeeding field, thus all the odd numbered fields contain one set of scan lines and the even numbered fields contain the set of scan lines which interlace with the scan lines in the odd numbered fields. This arrangement permits the transmission, reception, and picture reproduction at bandwidths reduced from that required for every scan line to be transmitted in each field.
Television pictures reproduced in these conventional systems have aspect ratio of four to three, i.e. for every four units of horizontal width there are three units of vertical height. Thus, a picture tube 15 inches on the diagonal has a width of 12 and a height of 9 inches, while a picture tube 19 inches on the diagonal has a width of 15.2 inches and a height of 11.4 inches.
The above specifications provide television pictures of good commercial quality which, however, degrade as the size of the picture tube increases. The graininess of the the picture produced by the 2:1 interlace ratio is acceptable for small screen receivers, but becomes more apparent as the the size of the picture tube increases. Consequently, as the television screens continue to increase in size the graininess becomes increasingly more unacceptable. To counteract this and provide greater picture resolution high definition television systems having increased aspect ratios and 1:1 progressive scans are presently under consideration.